The Environmental Features of the Monte Corchia Cave System (Apuan Alps, Central Italy) and Their Effects on Speleothem Growth

International Journal of Speleology 37 (3) 153-172 Bologna (Italy) October 2008

Available online at www.ijs.speleo.it International Journal of Speleology Official Journal of Union Internationale de Spéléologie

The environmental features of the Monte Corchia cave system (Apuan Alps, central Italy) and their effects on speleothem growth

Piccini L. 1, Zanchetta G. 2,8, Drysdale R.N. 3, Hellstrom J. 4, Isola I. 5, Fallick A.E. 6, Leone G. 7, Doveri M. 8, Mussi M. 8, Mantelli F. 9, Molli G. 2, Lotti L. 10, Roncioni A. 11, Regattieri E. 11, Meccheri M. 12, Vaselli L. 13

Abstract: Piccini L., Zanchetta G., Drysdale R.N., Hellstrom J., Isola I., Fallick A.E., Leone G., Doveri M., Mussi M., Mantelli F., Molli G., Lotti L., Roncioni A., Regattieri E., Meccheri M. and Vaselli L. 2008. The environmental features of the Monte Corchia cave system (Apuan Alps, Central Italy) and their effects on speleothem growth. International Journal of Speleology, 37(3), 153-172. Bologna (Italy). ISSN 0392-6672.

The Monte Corchia cave system, one of the most famous and popular caves in Italy, has in recent times been the subject of investigation on its speleothems as paleoclimate archives. This paper describes the geology, geomorphology and water chemistry of the cave system with the aim to elucidate the processes that have generated these speleothems and the properties they contain that are so useful for paleoclimatology. Some general conclusions can be drawn: i) the Corchia system is a cave developed over different altitudes during progressive uplift of the mountain chain in which it is located, probably under drainage conditions very different to those of the present. This has allowed the development of a large (ca. 60 km) and deep (-1187 m) karst system; ii) the dewatering phases have left the deepest chambers far away from clastic input and with long drip pathways; iii) the peculiar geological context has permitted the water to intercept and dissolve a significant source of U (still unknown) that facilitates radiometric dating; iv) in the last 1 Ma at least, no significant changes have occurred in the relief and in the epikarst, in the sense that speleothems have grown under very similar conditions. In addition the extremely low Ca concentration of drip waters have permitted low speleothem growth rates and, at least for the “Galleria delle Stalattiti”, the zone under paleoclimate studies, a stable plumbing system (i.e. chemistry and stable isotopes of drip waters) has produced calcite close to isotopic equilibrium. Keywords: speleothems, karst geomorphology, cave water chemistry, Corchia cave system, Apuan Alps, Central Italy. Received 12 February 2008; Revised 23 July 2008; Accepted 28 July 2008

INTRODUCTION deepest in the world at that time. In the second half Discovered on 11 October 1840 by Emilio Simi, a local of the last century, thanks to its relevant development naturalist, the Monte Corchia cave system has long and depth, the Monte Corchia Cave attracted hundreds been one of the most famous and popular caves of Italy. of speleologists from Italy and abroad. In the 1980s Initial surveying of the cave dates to the second half of the collaboration and, at times, the competition among the 19th century, but serious exploration began only at several Italian caving groups allowed the exploration of the beginning of the 20th century. In 1934, cavers from about 60 km of cave passages, thanks to the connection Florence attained what they believed to be the bottom of different caves belonging to the same karst system, of the cave, at about 540 m below the entrance, the with the depth reaching 1187 m.

1 Dipartimento di Scienze della Terra, University of Firenze, 7 Dipartimento dell’Uomo e dell’Ambiente, University of Pisa, Via la Pira 4, 50121 Firenze, Italy. Via delle Belle Torri 18, 56127 Pisa. E.mail: [email protected]. 8 Istituto di Geoscienze e Georisorse, Area della Ricerca CNR di 2 Dipartimento di Scienze della Terra, University of Pisa, Via S. Pisa, Via G. Moruzzi 1, 56124 Pisa. Maria 53, 56126 Pisa, Italy. 9 Agenzia Regionale per la protezione Ambientale della Toscana 3 School of Environmental and Life Sciences, University of (ARPAT) – Dipartimento Provinciale di Firenze. Newcastle, Callaghan, NSW 2308, Australia. 10 Agenzia Regionale per la protezione Ambientale della 4 School of Earth Sciences, University of Melbourne, Parkville, Toscana (ARPAT) – Dipartimento Provinciale di Massa. Victoria 3010, Australia. 11 Gruppo Speleologico Lucchese, Lucca Italy. 5 Istituto Nazionale di Geofisica e Vulcanologia, Sez. di Pisa 12 Dipartimento di Scienze della Terra, University of Siena, via Via della Faggiola, 32, 56100 Pisa. Laterina 8, I-53100 Siena, Italy 6 Scottish Universities Environmental Research Centre, East 13 Istituto di Geoscienze e Georisorse, UO Pisa, Via S. Maria Kilbride, Scotland. 53, I-56126 Pisa Italy. 154 Leonardo Piccini et al.

The Monte Corchia massif, which hosts the entire GEOGRAPHICAL AND GEOLOGICAL cave complex, is a site of historical and modern FRAMEWORK marble exploitation. It is part of the vast district of the Alpi Apuane, which has yielded some of the Location and geographic framework most famous ornamental marbles in the world. Monte Corchia is located in the south-western part Marble exploitation, speleological activity and cave of the Alpi Apuane (NW Tuscany, Italy), a mainly preservation have never quite found a complete calcareous mountain range about 50 km long, 20 equilibrium. km wide and up to 1947 m high (Fig. 1). The alpine- In the recent past (1985), the area of Monte like landscape of this peculiar region is due to Corchia has been included in the Alpi Apuane several factors. In particular, the complex structural Regional Park and on 4 August 2001 part of the cave setting, characterized by very steep bedding and the system was opened to the public after three years of tectonic repetition of different rocks (mainly limestone construction work. The opening of the tourist cave and phyllite), has enhanced the role of differential has not completely cooled the struggles between erosion. the defenders of this natural heritage and “the The present topography is presumed to be the result quarrymen”, but it has shown that local economic of heavy fluvial erosion accompanied by rapid tectonic benefits can arise from using this landscape without uplift during the Early Pleistocene (Piccini et al., 2003; the need to extract marble. Bartolini, 2003). Glacial and periglacial processes The Federazione Speleologica Toscana (Tuscan reshaped the landscape mainly during the last two Speleological Federation) understood the new glacial stages, emphasising the “alpine-like” features potential of easier accessibility to the cave, and of this mountain range (Braschi et al., 1986). has logistically and economically supported (since A large part of the Alpi Apuane consists of carbonate 1998) palaeoclimate research using speleothems. rocks. Despite this, only a few large-scale karst The ongoing research has demonstrated that a new landforms occur, while medium and small-scale scientific “adventure” has now begun (e.g. Drysdale landforms are widely represented. The present effects et al., 2004, 2005, 2007; Zanchetta et al., 2005, of karst processes on the landscape are limited, since 2007). the high relief enhances the role of physical degradation The potential of this cave for paleoclimatological by running waters and cryogenic processes along studies is huge. Data so far obtained suggest that it the higher ridges. On the contrary, in the past a would be possible to obtain a continuous record as subdued relief has permitted the development of a far back as 1,5 Ma from stalagmites and flowstones more advanced exokarst and of large cave systems; (e.g. Woodhead et al., 2006) using U/Th, U/U and therefore, most of the major karst landforms and U/Pb systematics. The stalagmites so far studied caves are relict forms (Piccini, 1998). have preserved in their oxygen isotope composition a detailed record of past climatic changes, Local climate which mimics the sea-surface temperature over The Alpi Apuane is one of the rainiest areas in the Western Mediterranean and North Atlantic Europe. Mean annual rainfall exceeds 2500 mm over (Drysdale et al., 2004, 2005, 2007). a large part of the chain and on the central ridges it The δ18O values of calcite usually increase is more than 3000 mm/yr (Rapetti & Vittorini, 1994; during colder periods and decrease during warmer Piccini et al., 1999). The Corchia area is surrounded and wetter phases, probably due to the effects of by six official meteorological stations, located at the changes in precipitation amount (the so called villages of Retignano, Terrinca, La Polla, Campagrina, “amount effect”). Growth rate is an additional Isola Santa and Fornovolasco (Fig. 1). Table 1 shows climate proxy for these speleothems in its own the long-term mean precipitation in these localities; right (Drysdale et al., 2007), mirroring δ18O time Campagrina, very close to Monte Corchia, has a mean series. The δ13C of Corchia speleothems seems to annual precipitation of 3055 mm, one of the highest record climatic perturbations superimposed over values in Italy. soil evolution above the caves, usually correlating Monte Corchia is part of the main drainage divide, positively with δ18O during cold excursions. During which separates rivers flowing to the coastline of the transition from a glacial to an interglacial, Mar Ligure from those flowing to the interior basin there is an interesting lag observable, probably Elevation Mean rainfall due to delay in soil development over very rugged Station and steep relief. (m a.s.l.) (mm/yr - 1951-2000) This paper is a collation of the works conducted Terrinca 485 1830 by many specialists who are currently working Retignano 440 1910 on this cave system from several points of view. La Polla 600 2240 In the last years the study of Corchia speleothems Campagrina 850 3055 has brought together scientists from different Isola Santa 585 2620 fields, and this paper represents the first holistic Fornovolasco 470 2395 contribution on the cave and its environment and explains why it preserves such relevant records of Table 1 - Mean annual precipitation in the meteorological stations past climate changes. nearby the Mt. Corchia.

International Journal of Speleology, 37(3), 153-172. Bologna (Italy). October 2008 The environmental features of the Monte Corchia cave system and their effects on speleothem growth 155

Fig.1. Location map of the studies area. Rainfall station lower panel: 1) Retignano; 2) Terrinca; 3) La Polla; 4) Campagrina; 5) Isola Santa and 6) Fornovolasco. of the Serchio River. For this reason, its climate is when melt water adds to rainfall, and the autumn, the characterized by variations as a function of elevation most rainy period, when temperatures are low enough and distance from the sea. to reduce evaporation and the trees have already lost Although rain usually increases with altitude, the their leaves, reducing the amount of interception by rainfall registered by stations located in the most vegetation. entrenched valley and just beyond the mountain Fig. 2 shows the precipitation at 1000 m on Monte crests, such as Campagrina, Isola Santa and Corchia obtained with the mathematical expression Fornovolasco, can be considered as representative of proposed by Piccini et al. (1999), compared with an upper elevation. infiltration estimated by taking into account the According to Piccini et al. (1999), the mean accumulation of snow during winter and its melting precipitation in the whole hydrogeologic system of during the spring season based on mean daily Monte Corchia is 2650 mm/yr (based on data from temperatures. The proposed altitude is roughly 1951 to 1995), while infiltration, calculated using the the average of that where infiltration feeds the cave Thorntwaite method and assuming a mean infiltration system. rate of 55%, is estimated at ca. 1150 mm/yr. In the Mean temperatures are difficult to estimate because upper area of Monte Corchia, where the cave system of the lack of long-term meteorological monitoring is located, the mean annual rainfall is around 3000 in the high-altitude zones. The only thermometric mm, with an effective infiltration of ca. 1500-1600 station is at Retignano, which is located at 440 m mm/yr. a.s.l. on the southern side of the mountain and so it Regional rainfall is concentrated in autumn and cannot be considered representative of the whole area. spring, but a real dry period does not occur. An Air temperatures measured in two stations installed estimation of annual distribution of infiltration has by Azienda Regionale Protezione Ambiente Toscana to take into account of the fact that in winter most (ARPAT) supply the values reported in table 2, which of the precipitation occurs as snow, which persists refer to the year 2002. until March-April. For this reason infiltration is It is probable that the cave itself provides the concentrated during two periods: the early spring, best estimate of mean annual temperature of the

International Journal of Speleology, 37(3), 153-172. Bologna (Italy). October 2008 156 Leonardo Piccini et al.

N° of hourly Meteorological Mean Air Temperature Elevation Mean airspeed measurements Station (ARPAT) (°C ±1σ) (m a.s.l.) (m s-1 ± 1σ) considered Tourist entrance 11.8 ± 6.9 860 0.8 ± 0.8 78 420 Mt. Corchia crest 7.8 ± 7.2 1480 2.1 ± 1.7 13 880

Table 2 – Mean values of air temperature and wind speed, recorded in two meteorological stations located on Mt. Corchia (for the location see Fig. 5). Data refer to 2002 onward.

dolostones (“Grezzoni”), dolomitic marbles and marbles (the famous “Carrara marbles”), which are followed by Upper Liassic-Lower Cretaceous cherty metalimestones, cherts and calcschists. Lower Cretaceous to Lower Oligocene sericitic phyllites and calcschists, with marble interlayers, are related to deep-water sedimentation during drowning of the former carbonate platform. The Oligocene-Early Miocene (?) sedimentation of turbiditic metasandstones (“Pseudomacigno”) closes the sedimentary history of the domain. The Alpi Apuane deformation structures are interpreted as formed by two main tectono-metamorphic regional events (D1 and D2 phases of Carmignani & Kligfield, 1990), which are regarded as a progressive deformation Fig. 2. Graph showing monthly temperature, rainfall and estimated of the inner Northern Apennine continental margin infiltration on Mt. Corchia area. during collision and late to post-collision evolution (e.g. Molli & Meccheri, 2000; Molli & Vaselli, 2006). During mountain area. According to the temperatures D1, SW to NE directed overthrusts and NE-facing tight registered during the cave monitoring (table 3) to isoclinal recumbent folds with flat-lying axial surfaces and taking into account the fact that mountain were produced during deformation in mid-crustal caves temperatures are commonly depleted by cold conditions. In the following D2 history previously formed infiltration waters, the mean annual temperature structures were refolded and the present-day geometry at 1000 m a.s.l. should be ca. 7-8 °C in the north of the tectonic units and structures was achieved. In the facing sides and ca. 8-9 °C in the southward sides. early stage of D2, folds associated with sub-horizontal crenulation axial foliation were formed, whereas later Geology deformation was associated with semi-brittle and brittle The Alpi Apuane represents a tectonic window structures, represented by kink and open folds, low- that shows the deepest exposed levels (Tuscan and high-angle faults (Molli & Meccheri, 2000; Ottria & Metamorphic Units) of the Northern Apennines. The Molli, 2000). Northern Apennines are formed by a pile of tectonic According to available P-T data (Molli & Vaselli, units derived from the distal part of the Adriatic 2006 and references therein), peak metamorphism continental margin (Tuscan Domain) lying below the (temperature around 450-350 °C and pressure of 0.8- westerly-derived “oceanic” Ligurian and sub-Ligurian 0.6 GPa) and early deformation D1 were realized at accretionary wedge units (e.g. Elter, 1975; Carmignani 27-20 Ma (Kligfield et al., 1986), while early stages of & Kligfield, 1990; Molli & Vaselli, 2006 and references D2, developed at T higher than 250 °C, predated 11 Ma therein). according to the zircon fission-track data of Balestrieri Two major tectono-metamorphic units are et al. (2003) and Fellin et al. (2004). The latest stages traditionally distinguished in the Alpi Apuane region: of deformation, accommodating vertical movements the Massa unit and the Apuane unit. A Palaeozoic locally exceeding 4 km, are achieved in the last 5 Ma as basement with a Mid-Triassic succession and the constrained by low-temperature thermochronometry, higher-grade peak metamorphic assemblages, which suggests the transition at 120-100 °C at between kyanite+chlorithoid in metapelites (references in Molli 4 and 5 Ma in most of the metamorphic tectonic window & Vaselli, 2006) characterize the Massa unit, which (Abbate et al., 1994; Fellin et al., 2007 and references is well exposed in the westernmost part of the Alpi therein). Apuane. On the contrary, the Apuane unit shows a THE KARST SYSTEM lithostratigraphic sequence made up of a Palaeozoic The geological structure of Monte Corchia is very basement (mainly phyllites and metavolcanics) complex and its 3D form is difficult to visualise. In unconformably overlain by a well-developed Upper any case, the karst system is well delimited, being Triassic-Oligocene metasedimentary succession. The developed inside the carbonate core of the Corchia Mesozoic cover includes Triassic continental to shallow syncline, almost completely enclosed by the non- water deposits (“Verrucano”) followed by Upper Triassic- karstifiable, low permeability basement (Fig. 3). The Liassic carbonate platform metasediments comprising presently known cave system occupies the northern

International Journal of Speleology, 37(3), 153-172. Bologna (Italy). October 2008 The environmental features of the Monte Corchia cave system and their effects on speleothem growth 157

Fig.3. Geological map and cross profile of Mt. Corchia.

International Journal of Speleology, 37(3), 153-172. Bologna (Italy). October 2008 158 Leonardo Piccini et al. part of this geological structure, while in the southern major conduits, which represent the main collectors, and lower sector, which corresponds to the Monte Alto whereas the secondary branches are mostly developed ridge, there are no relevant explored caves. along fractures oriented about N-S. About half of the cave passages were originated Geologic setting under phreatic or epiphreatic conditions, in places The geology of this area has been the subject of strongly modified by vadose incision or by local investigations since the late 1800s (Lotti, 1881; breakdown. These conduits are organized as a Zaccagna, 1932). At that time, with a simplified complex 3D network distributed from 1550 to 450 m structural interpretation, the presence of east-dipping a.s.l., having the shape of regular tubes or canyons Mesozoic rocks between the Palaeozoic exposures (Fig. and with a mainly horizontal pattern (Fig. 4). 3) was related to a west-facing overturned syncline. A Due to percolation or vadose flows, several high- similar interpretation, followed later by Maxwell (1956), gradient passages intersect the epiphreatic networks was rejected by Carmignani & Giglia (1983). According along the main fractures. These vertical caves, which to these latter structural studies, the Corchia structure show the typical features of deep alpine karst and are is the result of polyphase deformation during which an common features in the other areas of Alpi Apuane, originally non-cylindrical eastward facing overturned are the present active drainage system from the syncline (D1) was refolded up to the present geometry surface to the main collector level. showing the downward directed sense of younging. The upper entrance is part of a steep canyon The structural map and cross-section of Fig. 3 intercepted by surface erosion and modified by several enlighten some of the major features of the geology collapses. The canyon is a relict form, probably fed by of the Monte Corchia area. A lateral termination of a surface basin now completely destroyed by erosion the D1 syncline is well exposed in the northern part, (Piccini, 1991, 1994). At 1400 m a.s.l. the canyon between the Monte Corchia peak and Fociomboli, encounters a well-developed level of relict phreatic where the hinge zone of the D1 Corchia syncline is tubes, locally modified by rock falls, which develop from exposed. In this zone, minor M-structures and the NW to SE, following the structural direction of main related axial plane greenschist foliation are refolded cleavage. Trending to the SE, after a SW-NE oriented, by open to tight east-facing D2 folds associated with long and deep canyon, phreatic morphologies become a sub-horizontal crenulation cleavage. The youngest dominant and the galleries display well-preserved rocks in the core of the syncline are the late Jurassic sections of elliptical tubes. cherty metalimestone in the northern part and the late The morphology of these galleries suggests a recharge Jurassic to Cretaceous calcschist, metaradiolarite, by allogenic waters, which deposited conglomerates chloritic marbles and Oligocene metasandstone in the with well-rounded exotic pebbles. These pebbles southernmost part of the map. consist of non-metamorphic sandstone coming from About 55% of Corchia Cave is developed in Triassic the Tuscan or Ligurian nappes, a lithology that does dolostone and 40% in Jurassic marbles, whereas 5 % of not outcrop in the present day cave catchment area, cave passages are carved in the cherty metalimestone, which thus implies a morphological setting very “Brecce di Seravezza” or dolomitic marble. The different from the present one (Piccini, 1991, 1998). boundary between dolomite and marbles does not To the SE, the level closes with a large non-penetrable seem to represent an important geological horizon for rockfall. In the last part, the conduit system preserves the origin of the cave. Only in the northeastern sector some ancient calcite deposits, now heavily altered and are there passages that follow the contact between mostly broken because of the gravitational collapse of marble and dolomite. the cave wall. An analysis of cave passage orientations shows that Different generations of high-gradient caves cut this the highest and oldest level is more influenced by paleo-phreatic level, many of which are active and lithological planes, whereas the lower and youngest are the present pathways of local infiltration water. levels are controlled mainly by fracture patterns. More than one connection reaches a lower, almost This can be explained assuming that the first stage horizontal level of phreatic tubes, which is located at of cave development occurred when the relief was not an altitude of ca. 1300-1350 m. This level has a most so accentuated and the permeability of fractures was irregular plane pattern without significant diversion. reduced by lithostatic load (Piccini, 1991). All parts of the cave system described above are completely carved in marble. Cave geomorphology In the north-western part of the cave, one of the The Corchia cave system occupies a volume of rock vadose entrenchments descends northward and about 2 km long, 1 km wide and 1 km high, gently reaches a second and more developed level of phreatic dipping towards the SE. The system now has 14 and epiphreatic conduits at 1200-1150 m a.s.l. Most entrances, the highest of which is named “Buca del of these galleries are carved in dolomite (Grezzoni). The Cacciatore” and opens at 1637 m a.s.l., just a few tens pattern is complex, and it is often difficult to recognize of meters below the summit of Monte Corchia. The the main conduits from secondary ones. geological structure strongly controls the pattern of In the SE sector the upper system of phreatic conduits the cave, which is roughly elongated according to the (1450-1300 m a.s.l.) trends gradually down along large main axial surface, that is to say along the strike of galleries heavily modified and incised by free flow of a lithological beds and main cleavage. This is true for the large quantity of water. This large canyon intersects

International Journal of Speleology, 37(3), 153-172. Bologna (Italy). October 2008 The environmental features of the Monte Corchia cave system and their effects on speleothem growth 159

Fig.4. Sketch profile of Mt. Corchia cave system. 1) Main entrances, 2) phreatic and epiphreatic passages, 3) vadose passages. the major phreatic level of the karst complex at 1100- The hypogean climate 1200 m a.s.l. This level was probably connected with The interior climate of a complex cave system depends the NW section to form a single and ramified system on several factors. In general, the temperature is of phreatic galleries. Deep canyons entrench some of mainly controlled by infiltration waters, and, secondly, these phreatic tubes, indicating a long phase of vadose by geothermal heat flux and airflow circulation incision close to the hydrological base level. Some (Mavlyudov, 1997; Badino, 2004). The flow of water vadose pathways lead to a further level of phreatic in the vadose zone is very rapid. Consequently, the conduits located about 200 m below, between 900 hypogean isotherms are depressed with respect to and 800 m. The third cave level is still active in the the external ones. For this reason, the temperature of inner part of the system, where an underground cave passages far from the external surface is usually stream, whose mean discharge is presently around some degrees lower than the external temperature at 0.15 m3/s, flows in partially water-filled conduits. This the same elevation (e.g. compare table 2 and table 3). circumstance is due to the occurrence of a structural Relative humidity is usually close to 100% and dam that consists of low-permeability rocks (“Brecce fluctuations are within the sensitivity of the humidity di Serravezza” and “Scisti a Cloritoide”). Downstream instruments employed. Airflow is present due to of this structural obstacle the subterranean stream the numerous entrances of the system. The present deepens with a long active canyon stepped by a series number of entrances is largely unnatural because of waterfalls up to 40 m high. At an altitude of 600 of the opening and enlargement of several entrances m, the stream encounters a further level of water- due to quarrying and the exploration activities of filled phreatic conduits, which indicates another local cavers. However, the elongated plan shape of some perched piezometric level. stalagmites (e.g. at the so called “Foresta Pietrificata”, The stream flows along an unknown path, and then part of the branch called “Galleria delle Stalattiti”) re-appears in the last section of the cave at 600 m suggests a long period of strong airflow in ancient a.s.l. The cave stream deepens towards the SE along times. Conversely, in the more recent past, before the a vadose canyon with a step-and-pool morphology openings of the first artificial entrance (1841) and the until it reaches the present bottom of the cave, enlargement of lower entrances of the cave systems at 450 m a.s.l. by cavers (especially from 1973 to 1990), the airflow

Elevation Mean Air Temperature Mean humidity Mean air speed N° of hourly measurements ARPAT Station (m a.s.l.) (°C ± 1σ) (% ± 1σ) (m s-1 ± 1σ) considered Station 1 875 7.4 ± 1.2 99.8 ± 0.1 0.12 ± 0.10 106 539 (Galleria Franosa) Station 2 830 8.3 ± 0.2 99.9 ± 0.1 0.10 ± 0.08 98 131 (Galleria del Venerdì) Station 3 840 8.4 ± 0.3 100.0 ± 0.2 0.09 ± 0.07 48 500 (Galleria delle Stalattiti)

Table 3 – Mean values of air temperature, humidity and wind speed, recorded in the three stations. The data refer to the period 2002-2006, for which the data set is more complete. For station location see Fig. 5.

International Journal of Speleology, 37(3), 153-172. Bologna (Italy). October 2008 160 Leonardo Piccini et al.

Fig. 5. Location of sampling sites on Mt. Corchia and inside the cave.

should have been relatively low because most of the cave entrances were blocked by debris. Presently, the airflow along cave passages close to entrances (up to 200 m) is influenced by external temperature and is subject to condensation or evaporation processes. Sufficient meteorological data are available only along the tourist path where three monitoring stations of ARPAT are located (Fig. 5). This sector (about 2 km in length) is characterised by passages with large cross-sections. In the proximity of station 2, mean air speed is ca. 0.10 ± 0.08 m/s. Considering a cross section of about 50 m2 and assuming the air velocity uniform over the whole section, this corresponds to about 5 m3/s of air discharge. Fig. 6 shows the air movement over the caves obtained from monitoring and the direct observations of cavers during winter and summer circulation. Table 3 summarizes the temperature, moisture and air velocity data at the three stations in the cave. Typical fluctuations emphasize the extreme stability of stations 2 and 3 with respect to air temperature and relative humidity, as expected for a deep sector of the cave. Note that station 1 has a mean annual temperature significantly lower than Fig. 6. Schematic airflow directions in the cave system, during winter the other two due to the fact that it is located near and summer conditions, as obtained by monitoring and cavers two lower entrances through which cold air enters reportages. during winter.

International Journal of Speleology, 37(3), 153-172. Bologna (Italy). October 2008 The environmental features of the Monte Corchia cave system and their effects on speleothem growth 161

General hydrology upper and less known sectors of the karst system The hydrological structure of the Corchia karst (Fig. 5). Here we summarize the most relevant system consists almost exclusively of the carbonate chemical features of waters. core of the Monte Corchia-Monte Alto syncline, which is cut by the Torrente Vezza. The karst area is Rainfall and runoff waters well defined, being bordered by a belt of Palaeozoic Table 4 shows the mean concentration of the basement. No significant allogenic recharge occurs, major ions measured in rainfall samples collected except for some small inputs in restricted areas on irregularly from 1997 to 2006 at a station located the east side of Monte Alto and in the lower part of at 1074 m a.s.l. on the SW side of Monte Corchia the hydrological system. Dolomite and marbles are (Mantelli et al., 2001, 2003, 2005; Fig. 1). Table 5 the main karst aquifers. shows the chemistry of surface runoff collected The catchment area is well constrained from dye irregularly on the W slopes. These waters were tests performed by the Federazione Speleologica usually collected in ephemeral streams soon after Toscana (Roncioni, 2002, and references therein). or during significant rainfall events. Figure 7 shows A recent experiment appears to exclude that Omo a comparison between the averaged composition of Salvatico cave, in the north of Monte Corchia, local rainfall and those of surface runoff. It is obvious belongs to the recharge basin of Corchia system, as that the most significant ion enrichment to the runoff 2+ - previously supposed on the basis of earlier dye tests waters is attributed, as expected, to Ca and HCO3 . (Roncioni, 2002). Cl-, Na+, and K+ concentrations are virtually identical 2- The springs are located in the valley of Torrente to that of rainfall, while the SO4 contribution from Vezza, a few hundred meters upstream of Ponte the rainfall seems to be modest. Stazzemese, at 176 m a.s.l. Water rises from several points in the left side, which is the opposite side with The cave waters respect to the Corchia system, of the Vezza stream, a Flowing waters few meters above the riverbed. Here there are several The general geochemistry of flowing cave waters springs mantled by slope rock-fall, some perennial is determined by the interaction with the host and some occasionally active, which together are carbonate rocks, producing Ca-bicarbonate waters named “Le Fontanacce”, or “Cardoso” springs (Fig. Average Range 1). Ion A precise measure of discharge is difficult, due to (mg/l) (mg/l) the disperse outflow of this group of springs, which Cl- 3.7 9.9÷1.0 - are distributed along the riverbed. Bibliographic NO3 1.8 3.6÷0.8 2- sources (Piccini, 2002, and references therein) SO4 2.8 7.3÷0.2 indicate discharges usually ranging from 0.06 to - HCO3 6.4 38.0÷<5.0 3 0.26 m /s, with minimum values of 0.010-0.015 Na+ 2.7 9.5÷0.3 3 3 m /s, but flood flows up to 3 m /s. On the basis of K+ 0.4 4.0÷0.1 the few measurements available, the mean discharge Ca2+ 3.0 9.0÷0.8 3 is thought to be about 0.12 m /s. Mg2+ 0.4 2.4÷<0.1 The cave stream disappears at the bottom of the cave, under a rock collapse, at an altitude of 450 Table 4 - Minimum, median and maximum values of major ions in the m a.s.l. and about three km from Cardoso springs rain water, sampled since 1997, on the SW ridge (1074 m a.s.l.) of (Fig.1). We have no information about the last part Mt. Corchia. See Fig. 5 for the location. of the underground drainage, but the flow should be mainly phreatic. The elevation change from the cave bottom to the spring is probably due to the recent downcutting of surface drainage and testifies to a non-equilibrium state of the karst system with respect to the present base level (Piccini, 1998). Piccini et al. (1999) have computed the hydrologic balance of the karst system. The surface catchment area is about 7 km2. According to these figures the mean discharge of the springs should be about 0.3 m3/s, instead of 0.12 m3/s. The difference is probably due to the occurrence of hidden springs along the streambed of the Vezza river.

WATER GEOCHEMISTRY In the last ten years, several chemical analyses of rain, surface and cave waters have been performed. Most of the cave waters have been collected along the tourist path and the most visited parts of the cave, Fig.7. Comparison between the averaged composition of local rainfall although some samples have been collected in the and those of some superficial runoff waters.

International Journal of Speleology, 37(3), 153-172. Bologna (Italy). October 2008 162 Leonardo Piccini et al.

Tourist Stream below Stream above Station Canale delle Volte entrance tourist entrance Buca del Serpente Date 16/04/98 11/11/01 16/04/98 18/11/02 21/11/03 23/03/04 12/12/04 02/01/05 31/08/05 Conductivity 211 249 74 252 277 214 206 41.4 181 µS/cm 25 °C TDS (mg/l) 127 147 45 148 162 121 135 35 112 pH 8.2 7.8 8.1 7.8 7.1 8.0 7.4 6.6 7.2 + NH4 (mg/l) <0.1 <0.1 0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 - NO2 (mg/l) <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 0.02 <0.05 <0.05 Cl- (mg/l) 7.8 9.9 3.6 7.1 7.0 6.6 12.1 3.5 6.5 - NO3 (mg/l) <0.5 3.6 2.9 2.3 7.6 0.4 0.9 1.0 0.8 2- SO4 (mg/l) 11.5 17.5 9.8 13.8 23.7 18.1 15.0 2.4 19.7 - HCO3 (mg/l) 107 132 27.0 144 134 103 120 30 91 Na+ (mg/l) 3.8 4.4 1.7 5.1 5.3 4.2 6.5 1.8 3.4 K+ (mg/l) 0.2 0.2 0.5 <0.2 0.4 <0.2 1.0 0.6 0.7 Ca2+ (mg/l) 29.3 39.2 12.5 42.2 43.1 28.8 31.9 10.0 28.6 Mg2+ (mg/l) 8.2 7.0 0.5 6.7 7.0 9.3 8.7 1.0 8.5

Table 5 – Chemical analyses of running waters flowing outside the Corchia Cave system. For location see Fig. 5. with a variable amount of Mg, due to the presence CNR1 waters reflects contact mainly with marble. of dolomites (“Grezzoni”) and/or dolomitic marbles (Mantelli et al., 2005). Rainfall can principally Trace elements contribute Cl- and Na+ from marine aerosols (Mantelli Data on trace elements are few (Table 9) and concern et al., 2005). Sulphate is, in some cases, close to that mainly a sampling campaign carried out during 2006. of rainfall but enrichment compared to rainfall values Data from drip waters of CNR1 and CNR2 stations is probably related to oxidation of pyrite, a mineral (Fig. 5) reflect sampling conducted mainly during 2003. phase present within the Grezzoni. Of particular interest is the anomaly of some elements Table 6 shows a synthesis of the data obtained from the (e.g. Ba, Mo) and, notably, U in the drip point of CNR2 main flow of water from Cardoso Springs. A total of 108 and in the two pools of the “Galleria delle Stalattiti”. samples were collected from 1997 to 2007. For simplicity, Table 6 shows only the maximum and minimum values Stable isotope water geochemistry measured for each sampling station. From these figures, Several rainfall stations, whose stable isotope along with the comparison of the data presented in composition is well monitored, surround the area tables 4 and 5 and Fig. 7, it is possible to observe that of the Apuan Alps (Fig. 1). The data in table 10 mineralization of flowing waters starts soon with only a illustrate significant differences in the average isotopic minor increase at the terminal spring. composition of rainfall as one crosses from W to E over the Apennines; about 2‰ of difference exists between Pool waters stations located roughly at the same altitude. In detail, Table 7 shows a synthesis of chemical analyses of the spatial and temporal isotopic variability of local three different pools discontinuously sampled since 1997 meteoric precipitation has been inferred by Mussi et al. (see Fig. 5 for location). The pools of the “Galleria delle (1998) using isotopic data obtained from non-karstic Stalattiti” and “Laghetto del Venerdì” are fed by local drips springs with small catchments, which represent a and show a virtually constant chemical composition. good averaging of local infiltrating water because they For this reason, table 7 shows only the average values are unaffected by the event-scale changes in isotopic of their chemical composition. The pools of the “Galleria composition that can influence karstic springs. These delle Stalattiti” are characterised by a Ca-Mg bicarbonate data have been partially corroborated by results of 2- composition, with a higher SO4 content, in agreement analyses of rainfall collected at the S. Pellegrino in Alpe with waters derived from contact with metadolomite, the station (Fig. 1). Mussi et al. (1998) have shown that dissolution of which releases Ca and Mg, as well as the the altitudinal effect is variable according to mountain 2- SO4 from pyrite oxidation. aspect and they reported a pronounced E-W isotopic difference due to the typical travel path of vapour masses Drips producing a “rain-shadow effect” due to the Alpi Apuane Drip water samples have been collected sporadically and the Apennine chain. from different parts of the cave (especially in the area Doveri et al. (2005) reported the isotopic composition of the tourist path) but only for CNR1 and CNR2 are of drip waters collected in CNR1 and CNR2 stations into there enough data for a meaningful characterization Corchia Cave, highlighting the presence of two distinct (Table 8). The longest sampling period is for station sectors of the plumbing system probably characterised CNR2. The chemistry of CNR2 drips is extremely by different residence time, event sensitivity and recharge stable and characterised by a relatively high content area. Since the publication of Doveri et al. (2005) other 2- in Mg and SO4 , whereas the composition of data have been collected on the same drip points and

International Journal of Speleology, 37(3), 153-172. Bologna (Italy). October 2008 The environmental features of the Monte Corchia cave system and their effects on speleothem growth 163 in other parts of the cave, including flowing water, by seasonal effects and year-to-year rainfall isotopic pools and the terminal springs of Cardoso (Table 11). variability, which is averaged out in the case of CNR2. 2 Figure 8 shows the Corchia waters plotted on a δ HH2O- The carbon isotope composition of the dissolved 18 δ OH2O diagram. Almost all waters plot closely to the inorganic carbon (DIC) supports the notion of a different Central Mediterranean Meteoric Water Line (CMMWL), plumbing system and different residence time for the 13 with a deuterium excess (d) of 15 (Gat & Carmi, 1970; two CNR stations. The differences in the δ CDIC between Longinelli & Selmo, 2003). A few of the data points show CNR1 and CNR2 can be explained by a different input of lower d values without reaching the Global Meteoric biogenic (soil) CO2 via longer residence times for CNR2 Water Line (GMWL, with a d = 10). The spread of values station, which enhances water-rock interaction (Clark & is mainly due to CNR1 station, the drips collected at the Fritz, 1997), bearing in mind that local carbonate rocks entrance in the artificial gallery and the flowing waters have δ13C values ranging from 1 to 3‰ (Laurenzi et al., (the latter collected only once in March 2005). The lower 1982). However, the data are too few for drawing firm isotopic values, in particular those of the flowing waters, conclusions of the origin of δ13C of DIC, because soil can be explained by infiltration of water derived from discontinuity over the recharge area and prior calcite snow melting, usually characterised by lower d values precipitation (Fairchild et al. 2000) can play additional (Mussi et al., 1998) and, possibly, derived from higher role. altitude recharge areas. Figure 9 shows the oxygen isotope composition of DISCUSSION the drip stations CNR1 and CNR2 along with four Several geologic and environmental features make determinations of tritium content. In detail, the data show the Monte Corchia karst system one of the most the substantial stability of station CNR2 (mean: -7.4±0.1 promising caves in the world for paleoclimate research. ‰) and a significantly higher variability for station The evolution of the karst system probably includes CNR1 (mean: -7.3±0.4 ‰). The different behaviour of the entire Quaternary and possibly the Late Pliocene. the two stations is replicated by the tritium data. On the The age of fluvial deposits containing metamorphic hypothesis that there is no mixing of waters of different pebbles in the nearby subsiding basins (Calistri, ages, the tritium data suggest residence times of ca. 50 1974) suggests an exhumation age for metamorphic years for CNR2, and values consistent with precipitation carbonate rocks dating back to middle Pliocene. occurring within the year of sampling for CNR1. The Therefore, karstification is likely to have commenced data available do not support any significant differences just after this time. in the altitude of recharge (ca 0.1‰ on average between Several morphological features of the cave, along CNR1 and CNR2, which can locally represent less than with the occurrence of exotic pebbles, comprising 100 m), with the values of CNR1 likely to be influenced non-metamorphic lithologies in the most upper part of

2 18 Fig.8. The Corchia’s waters plotted in the δ HH2O-δ OH2O diagram. Almost all waters plot closely to the Central Mediterranean Meteoric Water Line (CMMWL) with a deuterium excess (d) of 15.

International Journal of Speleology, 37(3), 153-172. Bologna (Italy). October 2008 164 Leonardo Piccini et al.

Site Cardoso spring Gronda stream Vidal river Romani waterfall

Sampling date 23/03/04 29/09/04 05/09/01 13/02/07 22/07/03 13/02/07 14/05/98 24/03/00 Discharge (l/min.) > 1000 85 40 150 480 2400 60 120 T (°C) 10.0 10.8 8.2 7.7 7.1 6.9 7.8 8.9 Conductivity (µS/cm 25 °C) 221 278 250 216 219 201 188 223 TDS (mg/l) 125 153 138 120 155 113 100 118 pH 8.0 7.8 8.0 8.3 8.3 8.1 7.8 8.0 + NH4 (mg/l) <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 - NO2 (mg/l) <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 F- (mg/l) <0.1 0.1 <0.1 <0.1 0.2 <0.1 <0.1 <0.1 Cl-(mg/l) 6.6 7.0 9.2 6.5 4.8 6.7 3.9 12.1 - NO3 (mg/l) 1.6 2.7 1.6 0.8 1.7 1.1 2.7 2.6 2- SO4 (mg/l) 7.4 18.2 6.6 3.6 12.5 4.0 5.3 6.8 - HCO3 (mg/l) 126 138 141 129 121 116 98 107 Na+ (mg/l) 4.0 4.9 4.0 3.6 3.2 2.8 2.4 6.9 K+ (mg/l) <0.5 0.5 0.9 <0.3 0.3 <0.3 <0.3 <0.3 Ca2+ (mg/l) 32.4 38.7 32.3 27.3 27.4 30.3 31.6 30.6 Mg2+ (mg/l) 8.4 10.5 11.0 11.4 11.0 7.9 2.7 5.0

Table 6 – Chemical composition of Corchia cave flowing waters. Only the maximum and minimum measured value is shown (see fig. 5 for location).

Galleria Galleria Laghetto Pool the cave (Piccini, 1998), indicate that the karst system bassa alta Venerdì originated in a geomorphic framework very different N. of analyses 10 13 9 from the present one, probably before or during the Conductivity (µS/cm 25 °C) 318±6 326±8 271±6 first stage of uplifting of the Apuane range (Piccini, TDS (mg/l) 182±6 179±4 142±4 1998; Bartolini, 2003). pH 8.2±0.1 8.1±0.2 8.2±0.1 This hypothesis, which is becoming more consistent + NH4 (mg/l) <0.1 <0.1 <0.1 according to the oldest dates so far obtained from - NO2 (mg/l) <0.05 <0.02 0.05 speleothems in the Monte Corchia cave system (Woodhead Cl- (mg/l) 6.0±0.5 5.6±0.6 6.6±0.6 et al., 2006; unpublished data), conflicts with fission track - dating of less than 2 Ma, obtained in the most southern NO3 (mg/l) 4.7±2.1 3.3±1.9 4.6±0.4 2- part of the metamorphic window (Abbate et al., 1994), SO4 (mg/l) 31.6±1.3 35.6±1.5 9.6±0.4 HCO - (mg/l) 154±5 158±10 148±5 which implies that this sector of the Apuan Alps was still 3 located very deep at the time of initial speleogenesis of the Na+ (mg/l) 4.3±1.0 4.1±0.5 4.1±0.6 Corchia Cave. K+ (mg/l) 0.9±0.7 0.4±0.1 0.4±0.6 Speleothems occur in several parts of the cave, from Ca2+ (mg/l) 30.3±1.0 29.5±1.7 28.4±1.4 the upper and older level (at 1500 m a.s.l.) up to the 2+ Mg (mg/l) 20.6±0.9 23.3±1.8 15.9±1.1 deepest passages (located at 450 m a.s.l.). Thus, there is Table 7 – Chemical composition of pool waters (see fig. 5 for potential for recovering calcite deposits belonging to the location).

Station CNR2 CNR1

Date 11/09/97 29/11/97 18/03/98 16/04/98 20/06998 02/1198 29/09/99 17/11/04 02/11/98 17/11/04 18/11/05 Conductivity 336 337 338 330 333 335 337 331 253 226 252 (µS/cm 25 °C) TDS (mg/l) 191 192 193 198 199 201 184 190 152 132 144 pH 8.1 8.2 8.2 8.2 8.2 8.2 8.1 7.8 7.9 8.0 8.1 + NH4 (mg/l) < 0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 < 0.1 < 0.1 < 0.1 - NO2 (mg/l) < 0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 < 0.05 < 0.05 < 0.05 Cl- (mg/l) 5.3 4.7 4.5 4.8 4.8 3.9 5.5 5.4 5.7 6.9 6.2 - NO3 (mg/l) 0.25 <0.5 <0.5 <0.5 <0.5 <0.5 0.6 0.6 0.9 1.3 1.2 2- SO4 (mg/l) 36.1 33.5 33.6 34.6 36.5 31.9 33.0 35.4 5.7 5.0 6.1 - HCO3 (mg/l) 165 167 171 165 168 168 167 168 144 135 148 Na+ (mg/l) 4.3 4.0 3.5 3.6 3.9 3.6 3.6 3.8 3.5 3.9 4.2 K+ (mg/l) 0.2 0.3 0.2 0.3 0.3 0.2 0.3 0.3 0.2 0.2 <0.2 Ca2+ (mg/l) 32.0 33.4 32.4 32.6 32.9 33.2 31.9 33.7 38.5 34.3 38.7 Mg2+ (mg/l) 22.1 21.7 21.9 22.2 21.8 21.4 22.3 23.0 7.2 8.3 8.9

Table 8 - Chemical composition of drips from CNR2 station (Galleria delle Stalattiti) and CNR1 (see Fig. 5 for Location).

International Journal of Speleology, 37(3), 153-172. Bologna (Italy). October 2008 The environmental features of the Monte Corchia cave system and their effects on speleothem growth 165

Galleria Galleria Cardoso Gronda Vidal Romani Laghetto Sample Bassa Alta CNR1 CNR2 spring Stream river waterfall Venerdì Stalattiti Stalattiti B 3.0 2.5 0.9 1.5 3.0 2.5 2.5 2.0 5.0 Al 1.9 0.8 0.9 1.3 25.8 7.0 12.4 - - V 0.16 0.21 0.15 0.11 0.33 0.15 0.27 <0.2 0.38 Cr 0.05 0.06 0.03 0.02 0.50 0.23 0.38 1.4 2.0 Mn 0.16 0.10 0.15 0.64 0.14 0.12 0.23 <0.2 <0.2 Co 0.22 0.16 0.18 0.19 0.16 0.15 0.14 <0.1 <0.1 Ni 0.74 0.48 0.37 0.51 0.71 0.46 0.43 - 1.1 Cu 0.13 0.05 0.02 0.13 0.12 0.10 0.32 <0.1 0.22 Rb 0.20 ------<0.1 3.1 Sr 78 ------20 55 Mo 0.11 0.33 0.13 0.20 8.09 3.31 2.22 <0.2 13.7 Cd <0.02 <0.02 <0.02 <0.02 0.07 0.03 0.02 - - Ba 4.3 1.2 2.8 4.4 12.7 5.4 6.8 5.1 30 U 0.36 0.55 0.30 0.13 7.50 6.09 1.46 0.04 7.72 As 0.21 0.17 0.11 0.13 0.23 0.13 0.25 - - Hg 0.02 0.01 0.01 0.01 0.02 0.01 0.01 - -

Table 9 - Selected trace elements composition for some Antro del Corchia waters (data are in ppb).

Elevation δ18O‰ δD‰ Sampling Sampling station d References (m a.s.l.) (V-SMOV) (V-SMOW) period Longinelli & Pisa 5 -5.51 -33.3 10.8 1993-1999 Selmo. 2003 Pontremoli 236 -5.34 -30.4 12.4 2000-2002 “ “ Parma 55 -7.73 -49.4 12.5 1995-2002 “ “ Modena 34 -7.51 -48.3 11.8 1999-2001 “ “ Bologna 54 -7.50 -48.8 11.3 1998-2001 “ “ S. Pellegrino in Alpe 1522 -7.68 -46.9 14.6 1993-1999 “ “ Rozanski et al.. Genova-Sestri 2 -5.78 -35.1 10.3 1961-1987 1993

Table 10 - Stable isotope composition of meteoric water around the Apuan Alps.

13 18 2 CNR 2 (16/03/05) -3.8 -7.4 -43 Sampling site δ CCO ‰ δ O H O δ H H O 2 TU 2 2 (date of sampling) DIC ‰ ‰ CNR 2 (04/01/04) -7.4 -45 CNR 2 (22/09/06) -7.4 -45 CNR1 (07/06/03) -7.8 ±0.1 -7.3 -43 CNR 2 (29/09/06) -7.5 -45 CNR1 (22/08/03) -7.5 ±0.1 -7.1 -43 CNR 2 (28/10/06) -7.4 -47 CNR1 (13/12/03) -8.4 ±0.2 -7.5 -45 CNR 2 (26/11/06) -7.5 -45 CNR1 (04/01/04) -7.3 -42 CNR 2 (10/12/06) -7.5 -45 CNR 1 (17/09/04) -6.9 -7.1 -43 CNR 2 (28/12/06) -7.4 -45 CNR 1 (16/03/05) -6.6 -49 CNR 2 (20/02/07) -7.4 -44 CNR 1 (16/04/05) -8.2 -51 Artificial entrance CNR 1 (22/09/06) -7.4 -44 (20/02/07) -6.8 -40 CNR 1 (29/09/06) 5.5 ±0.7 -7.2 -44 Artificial entrance (22/08/03) -7.2 -44 CNR 1 (28/10/06) -7.7 (-7.4) -49 (-47) Laghetto L 1 (16/03/05) -3.3 -7.2 -41 CNR 1 (26/11/06) -7.2 -43 CNR 1 (10/12/06) -6.9 -42 Laghetto L 2 (16/03/05) -4.6 -7.2 -41

CNR 1 (28/12/06) -7.0 -42 Laghetto L 1 (18/04/03) -10.4 -6.9 -39 CNR 1 (20/02/07) 4.0 ±0.6 -6.6 (-6.7) -35 (-36) Laghetto L 2 (18/04/03) -10.1 -6.9 -39 CNR2 (13/12/03) -4.0 ±0.2 -7.4 -46 CNR2 (22/08/03) -4.2 2.22 ±0.4 -7.4 -44 Cardoso spring (16/03/05) -7.8 -7.4 -45

CNR2 (07/06/03) -4.6 ±0.3 -7.5 -46 Cardoso spring (13/09/05) -7.1 CNR 2 (17/09/04) -3.1 ±0.1 -7.3 -43 La Gronda fall (16/03/05) -7.8 -9.0 -58 CNR 2 (24/09/04) -4.4 ±0.1 2.7 ±0.6 -7.4 -46 CNR 2 (16/04/05) -7.4 -46 Vidal river (16/03/2005) -5.4 -8.3 -50

Table 11 – Isotopic composition of Antro del Corchia waters. CNR1 and CNR2 are drip points.

International Journal of Speleology, 37(3), 153-172. Bologna (Italy). October 2008 166 Leonardo Piccini et al.

Fig.9. The variability of the oxygen isotope composition of the drip stations CNR1 and CNR2 along with four determination of tritium content. In detail data show the substantial stability of station CNR2 (mean: -7.4±0.1 ‰) and a relatively larger variability for station CNR1 (mean: -7.3±0.4 ‰). whole evolution history of the cave system, allowing the percolating water to take a longer travel path before reconstruction of the progressive dewatering stages of the reaching the chamber. This travel is partially developed karst system due to the lowering of regional base level. along the contact zone of “Grezzoni” and this basement. -2 Presently, the chemical and isotopic analyses have The high Mg and SO4 content of pools and drips focused mainly on the “Galleria delle Stalattiti”, part demonstrate the significant contribution from dolomite. of the third (800-900 m a.s.l.) level of the cave, which The chemical composition of CNR2 station and drip-fed is easily attainable through the tourist path. This pools in the chamber show consistent and stable values, is the sector where calcite concretions mostly occur in agreement with the presence of a stable plumbing and, therefore, where speleothem-based research was system as suggested by stable isotopes. initiated. Another interesting consideration is depicted by the Meteorological data indicate that this sector is relatively stable in terms of temperature, air humidity and air circulation (Table 3), in agreement with its deep position within the cave (ca. 400 m below the surface) and distance from natural entrances. The isotopic composition of the water (δD, δ18O and Tritium content) of one monitored drip (CNR 2 station, Fig. 9) indicates a stable and well-mixed plumbing system characterised by a relatively long (ca. 50 yr) residence time. Assuming this drip is representative of this sector of the cave, this implies that only persistent and relatively long-term (decadal) variations in the isotopic composition of local precipitation is capable of forcing a significant change in the isotopic composition of drip waters, and therefore the speleothem calcite. Data from other drip points, although most meaningful only for station CNR1, suggest a relationship between rock thickness above the drip points and isotopic variability. However, more drip points need to be monitored over the long term in order to prove this pattern. It is important to remember that the “Galleria delle Stalattiti” is geometrically overlain at the surface by impermeable basement of phyllites and metavolcanics, which are only superficially fractured.

Furthermore, alteration processes of silicates produce Fig. 10. Plot of Ca versus the molar ratio of Mg to Ca ((Mg:Ca)molar) clay minerals that prevent the potential for deep vertical for various percolation waters sampled from the eastern portion of infiltration of recharging meteoric water, obliging Corchia Cave. Gr = “Grezzoni”, Md = “Marmi Dolomitici”

International Journal of Speleology, 37(3), 153-172. Bologna (Italy). October 2008 The environmental features of the Monte Corchia cave system and their effects on speleothem growth 167 chemical composition of the Corchia waters in figure calcite precipitation (Fairchild et al. 2000) may also be 10, which shows a plot of Ca versus the molar ratio of important, where calcite precipitates in air-filled voids

Mg to Ca ((Mg:Ca)molar) for various percolation waters due to CO2 degassing. This will preferentially reduce sampled from the eastern portion of Corchia Cave. Ca2+ and leave the waters relatively enriched in Mg2+. Two important points can be enphasised regarding These processes of incongruent dissolution and prior these patterns. First, the waters have extremely low Ca calcite precipitation both increase (Mg:Ca)molar and concentrations, ranging from about 0.7 to 1.1 mmol/L. may serve as a useful palaeohydrological proxy within The similarly low values observed in the Cardoso the speleothems. springs, draining the Corchia catchment area, suggest Although based on a few samples, some that such low values are a regional phenomenon, and considerations can be also given about the contents probably reflect the thin and highly discontinuous of trace elements in percolation waters. Of particular overlying soil cover mantling the Corchia karst, which relevance is the higher U content of the drip water would reduce the input of soil CO2 during percolation at CNR2 compared to the other analysed waters, and therefore have a dampening effect on how much which helps in explaining the high concentration of carbonate bedrock can be dissolved. Such low Ca U in the speleothems collected within the “Galleria values help explain the low deposition rates observed delle Stalattiti” (from ca 2 to 18 ppm, Drysdale et al., in Corchia speleothems at all time scales (Drysdale et 2004, 2005, 2007; Zanchetta et al., 2007; Hellstrom al. 2005; Zanchetta et al. 2007). Secondly, the (Mg:Ca) unpublished data). molar of the percolation waters generally increases as A possible source of the high U (and other enriched one moves from the artificial entrance towards the trace elements) could be the small bodies of “Brecce “Galleria delle Stalattiti”. Part of the reason for this di Seravezza”, which occur occasionally at the contact is the transition from “Marmi Dolomitici” (dolomitic between marbles and Grezzoni. These rocks are marble) to “Grezzoni” (dolomite) along this traverse. rich in heavy metals and specifically samples from However, importantly it can also be attributed to the Mt. Corchia show U concentrations up to ca 7 ppm effects on the evolution of the percolation waters as they (Franceschelli et al., 1996). Our determination of U traverse increasing overlying bedrock thickness. Such concentration by alpha-spectrometry on one geological an increase implies that waters arriving into deeper traverse of Mt Corchia (Table 12) does not show a parts of the cave take a longer flow path and therefore particular U enrichment of “Brecce di Seravezza”. have longer residence times within the host rock. This However, based on the present position of “Brecce in turn can lead to incongruent dissolution, where di Seravezza” outcrops it is not easy to imagine a the waters acquire greater quantities of Mg due to the significant influence on the drip water at CNR2. different solubility of dolomite and calcite. Here, as the The tectonic contact between basement and carbonate dolomite rock dissolves, the waters become saturated succession is often strongly mineralised (and in the with respect to calcite but remain undersaturated past subject of extensive ore-deposit exploitation), with respect to the mineral dolomite. As more dolomite and can represent an additional or alternative source rock dissolves, the waters become supersaturated of U for the drip waters entering in the “Galleria with respect to calcite, causing precipitation of CaCO3 delle Stalattiti”. Recently, Cortecci et al. (2003) have and loss of Ca2+ from solution, while continuing to observed that high angle brittle-fault cataclasites dissolve CaMg(CO3)2. This increases the (Mg:Ca)molar are strongly enriched in Sr, Mn, Rb, Cu, Zn and Pb, of the percolation water. The fact that some of the suggesting the possibility of a different source of U.

“Galleria delle Stalattiti” waters exceed the (Mg:Ca)molar Indeed, a sample of these cataclasites collected on Mt of Grezzoni is a good evidence of this process. Prior Corchia show the highest U concentration (>4 ppm)

U 234U/238U Sample Geology ± error ± error (ppm) (activity) Q1-1 0.11 0.01 0.98 0.09 Q1-2 *0.07 ------Q1-3 *0.05 --. -- -- Q1-4 Brecce di Seravezza (Jurassic) 0.20 0.01 0.96 0.07 Q2-3 0.33 0.02 1.01 0.07 Q2-5 0.53 0.02 0.92 0.05 Q2-6 0.20 0.01 1.04 0.06 Q3 Schist (Paleozoic) 0.87 0.04 1.23 0.08 Q4 Schist (Paleozoic) 0.83 0.04 1.31 0.09 Q5 Marble (Jurassic) *0.01 ------Q6 Dolomite (Triassic) 0.94 0.03 1.46 0.06 Q7 Cherty limestone (Jurassic) 0.10 0.01 1.1 0.1 Q8 Fault cataclasite (Pliocene?) 4.64 0.11 1.06 0.04

Table 12 – U concentration and 234U/238U determination of rock samples from Monte Corchia succession, as determined via alpha spectrometry: *) at the limit of detection of 1 Bq/kg (0.1 ppm), therefore the 234U/238U activity ratio would not be reliable.

International Journal of Speleology, 37(3), 153-172. Bologna (Italy). October 2008 168 Leonardo Piccini et al. over the collected samples. Another potential source CC26: -1.5±0.4‰, with the latter excluding the of U could be represented by the basement itself, values of the Early Holocene). These differences, which consists mainly of phyllite and metavulcanite however, are based on the assumption that station with presumably high U content (data analysis is in CNR2 is representative of the whole set of drips in the progress and for some preliminary data see table 12). “Galleria delle Stalattiti” where all speleothems have The progressive weathering of the palaeozoic “roof” been collected so far, which is probably only true as a and its progressive erosion may have produced a first approximation. Different drips may have shown U-enriched residual soil, which was probably trapped small different chemical and isotopic compositions in the epikarst, and then washed by seepage water. as they were fed by different horizons, experienced However, more prospecting is necessary to localize the different mixing paths and traversed different sectors exact source of U. of the cave. The high concentration of U in the drip waters and Despite the offset, which can be produced by 13 in speleothems is accompanied by virtually absent CO2 degassing, the high δ C values are generally clastic contamination of speleothems, which show suggestive of low input of biogenic CO2 (Dulinski 230 232 [ Th/ Th]activity values >4000, a property, along with & Rozanski, 1990), which is in agreement with high U content, which makes these speleothems ideal the poorly developed soil cover over Corchia for U/Th and U/Pb dating (Woodhead et al., 2006), and in particular with the potential recharge and requiring for U/Th dating negligible correction area of the “Galleria delle Stalattiti”. However, procedures (e.g. Hellstrom, 2007). the mechanisms that are responsible today in No active stalagmite growth has been observed in producing low Ca and high Mg concentrations the “Galleria delle Stalattiti” and in areas located could be the same as those which produce high adjacent to the tourist path. Four years of attempts δ13C values of DIC (incongruent dissolution of in collecting active drip precipitates have failed at dolomite with associated precipitation of calcite both stations CNR1 and CNR2, a fact attributed to and prior calcite precipitation). Additional the extremely low Ca concentration of the source dissolution of marbles via sulphide oxidation (e.g. waters (Drysdale et al., 2004) but perhaps also due iron sulphide) can also play a role in increasing to the use of a glass substrate. However, the δ18O the isotopic composition of DIC (Spötl & Mangini, composition of a theoretical calcite precipitated in 2007). the chambers should be (using the modified version Recent U/Pb and 238U/234U dating of speleothems of the Craig 1965 equation, e.g. Hoefs, 2004) ca. -5.6 from this chamber suggest that phreatic activity over ‰, which is actually lower than the average δ18O the “Galleria delle Stalattiti” ceased prior to ca. 1 ka values of two Holocene speleothems collected from (Woodhead et al., 2006 and unpublished data). Over the same chamber (CC4: -5,0±0.3 ‰, n=80; CC26: 200 age determinations suggest almost continuous -4.4±0.2‰ n=794, see Zanchetta et al., 2007 for CC26 deposition over the entire middle to late Quaternary, analyses). Traverses performed on many speleothems with hiatuses occurring locally mainly during glacial of this chamber (e.g. Drysdale et al., 2004; 2007) maxima and/or during pronounced short cooling usually respond favourably to Hendy’s test (Hendy, phases (e.g. Drysdale et al., 2004; 2005; 2007). 1971), suggesting that calcite precipitation generally Despite the presence of hiatuses the possibility of occurs close to isotopic equilibrium, at least compiling a continuous record over the last 1 ka is, along the growth axis and taking into account the however, realistic. There are good reasons to think difficulty of sampling well-defined laminae in a slow that the “Galleria delle Stalattiti” did not experience growing speleothem. The discrepancy of ca. 1-0.6‰ dramatic changes during this period of time. The δ18O-enrichment of Holocene speleothem calcite most striking evidence is represented by the almost compared to the predicted value is within the range of constant values of δ13C through time, which varied offset reported (<1‰) by the compilation of McDermott in the last 1 ka between a range of ca -3 and +3 et al. (2005). This offset could be partly due, at Corchia, per mill, with the higher values occurring during to the progressive opening of new entrances by quarry glacial and lower during interglacials (e.g. Drysdale activity and cavers in the last decades, which may et al., 2004). The stable carbon isotopes seem to have modified air circulation even if this seems to suggest that soil never significantly contributed have relatively little influence in such a deep part of biogenic CO2 to the DIC pool during very old periods the cave. A further effect can be related to changes and that flow paths have continuously favoured a in land use, from open woodland to grassland in an long interaction with the karst rock in a situation in environment mostly devoted to grazing and then to which relief energy cannot have changed much, at marble exploitation: a case documented for nearby least for the period of speleothem growth. Although Alpi Apuane areas (Quiros Castillo, 2004). A similar the most important phase of speleothem growth offset is observed for the carbon isotope composition. predates the Holocene and is probably related to the At the measured pH (ca 8.2) the δ13C values of DIC Middle Pleistocene (Zanchetta et al., 2005), carbon of the drip water (-3.9±0.6‰) should be close to the isotopes do not suggest significant changes in the δ13C values of a calcite precipitated under equilibrium condition of the epikarst. The progressive decrease conditions (e.g. Clark and Fritz, 1997). The δ13C of growth within the “Galleria delle Stalattiti” is expected value of calcite is, however, lower than that probably related to natural hydrological evolution observed in Holocene stalagmites (CC4: -2.0±0.3‰; and progressive senescence of flow paths.

International Journal of Speleology, 37(3), 153-172. Bologna (Italy). October 2008 The environmental features of the Monte Corchia cave system and their effects on speleothem growth 169

CONCLUSION F. Malfatti, and the Gruppo Speleologico Lucchese for The “Galleria delle Stalattiti” is the sector of Corchia their friendships and help during fieldwork. We thank Cave where speleothem-based studies have been Kathleen R. Johnson for the revision of the first draft presently focused. Its accessibility and the higher of the manuscript. number of speleothems mainly drove this focus. Monitoring of this gallery has revealed that it is fed APPENDIX (MATERIAL AND METHODS) by drips with very constant chemical and isotopic The tourist cave has been monitored since 1996 composition, which indicate a well-mixed flow, with following a precise request of the Federazione relatively long residence time and stable conditions in Speleologica Toscana in order to assess the impact of terms of temperature and humidity. The speleothems tourist activity on the cave environment. This duty was have grown slowly owing to (presumably) persistently entrusted to the Regional Agency of the Environment low Ca concentrations in the waters and slow CO2 (ARPAT) which selected three sites for continuous degassing, which can be considered optimal conditions monitoring (after preliminary analyses) of temperature, for precipitation of calcite close to isotopic equilibrium. CO2 concentration, air movement (velocity), and

However, this situation prevents us from obtaining humidity. The CO2 concentration monitoring system paleoclimate records with sub-decadal resolution. suffered several problems of calibration, and past Indeed, the deep pathway and the long residence time measurements are not considered completely reliable of the plumbing system acts to smooth out short-term and are not discussed here. The three sites were (decadal-scale) variations in recharge δ18O. This is, selected as representative of conditions near the however, compensated for by the presence of U-rich cave entrance (station 1), intermediate conditions speleothems free of a detrital component. Although the (station 2) and very stable deep interior conditions source of the U is still unclear, it is possible to claim (station 3, “Galleria delle Stalattiti”). Since 2002, two that these positive characteristics of Corchia cave are meteorological stations were set up outside the cave certainly due to its particular geomorphological and (principally for measures of temperature, wind speed, geological evolution, which can be summarized as and rainfall amount). Collection of the data were follows: sufficient for describing the general pattern of the 1) A relatively old cave developed over different measured parameters but the period of maintenance altitudes during the progressive uplift of the chain, and the problems related to the cut off of power probably in condition of drainage very different than produced gaps in the data records. During the present allowing the development of very large and activity for preparation of the tourist cave and after deep passages; the opening, the water chemistry of running and drip 2) Dewatering phases that have left the deepest waters has been sporadically collected in several places chambers well away from clastic input and with long along the tourist passage. Since this time, the Istituto drip pathways; di Geoscienze e Georisorse-CNR (national research 3) Peculiar geological situation that has permitted council) of Pisa and the Earth Science Department the water to intercept and dissolve a significant source of the University of Pisa installed two stations (CNR1 of U that facilitates radiometric dating; and CNR2) for collecting drip waters for stable isotope 4) In the last 1 Ma at least, no significant changes and chemical analyses. Sampling was conducted have occurred in the relief and in the epikarst in a irregularly since 2003 up to the present. Since 1997, a way that speleothems have grown in very similar system for the collection and measurement of rainfall conditions. amount was established at the so-called Southwest The conditions discussed above seem to approach nose (1074 m a.s.l.) near the cave entrance of Buca the case of the qualitative models proposed by Fairchild del Serpente (Fig. 5 44° 01’ 27” nord; 10° 18’ 05’’ et al. (2007), and can explain the relationships est). Water collection is usually every three months, between the geomorphic condition (i.e. flow path) and according to local weather conditions. These samples speleothem properties (e.g. fabrics and chemistry), were considered suitable only for chemical analyses which can be found in some deep caves, as the Corchia and a new station for collection of rainfall samples case. for stable isotope is now in progress, even if local The size of the cave and the amount of speleothem isotopic composition of meteoric water is reasonably material collected so far (plus two recent flowstone well known (e.g. Mussi et al., 1998). drilling campaigns which have produced more than This large amount of data is now being organised 8 m of core) indicate we are only at the beginning of into a Geographical Information System based at the exploring this exceptional archive of past climate, the Istituto Nazionale di Geofisica e Vulcanologia (INGV) protection of which is as important as the discovery of of Pisa. its own geological secrets. Chemical analysis have been carried out at the ARPAT laboratory of Florence, for the major constituents ACKNOWLEDGEMENTS atomic absorbing spectrometry (AAS) has been used, We are indebt with Federazione Speleologica Toscana whereas for trace elements the AAS-GF and ICP-MS for its support during the last ten years and for funding have been used. Mantelli et al. (2002) have discussed this research. We must also thank the President of methodologies and analytical performances. the Parco delle Apuane (G. Nardini) and the Director The oxygen isotope composition of waters was

(Dr. A. Bartelletti), G. Ledda, G. Bruschi, L. De Cesari, obtained by the equilibration of water with CO2 at

International Journal of Speleology, 37(3), 153-172. Bologna (Italy). October 2008 170 Leonardo Piccini et al.

25°C (Epstein and Mayeda, 1953), while the isotopic Cortecci G., Dinelli E., Molli G. & Ottria G., 2003 - composition of hydrogen was carried out following a Geochemical evidence for fluid-rock interaction along modification of the procedure proposed by Coleman high angle faults in the Alpi Apuane, NW Tuscany, et al. (1982), which consists of reducing water to H2 Italy. Periodico di Mineralogia, 72: 35-47. using metallic zinc. The carbon isotope composition Doveri M., Leone G., Mussi M. & Zanchetta G., 2005. of dissolved inorganic carbon (DIC) were obtained Composizione isotopica di acque ipogee nell’Antro measuring the CO2 exsolved by water by progressive del Corchia (Alpi Apuane, Toscana nord-occidentale). adding an excess of H3PO4 followed by the CO2 Memorie Istituto Italiano di Speleologia, S. II, 18: extraction and purification using cryogenic traps under 119-132. vacuum. The 18O/16O, 2H/H and 13C/12C ratios were Drysdale R., Zanchetta G., Hellstrom J.C., Fallick A.E., measured using a Finnigan MAT 250 and a Micromas Zhao J.X., Isola I. & Bruschi G., 2004 – Palaeoclimatic 602C. The results are expressed using the well-known implications of the growth history and stable isotope δ‰-notation with respect to V-SMOW, whereas (δ18O and δ13C) geochemistry of a Middle to Late 13C/12C ratios are expressed respect to the V-PDB Pleistocene stalagmite from central-western Italy. standard. Analytical precision was ±0.1, ±1 and ≤ ± Earth and Planetary Science Letters, 227: 215-229. 0.3 ‰ for oxygen, hydrogen and carbon respectively. Drysdale R., Zanchetta G., Hellstrom J., Fallick A. & Determination of tritium content was done by means Zhao J.X., 2005 - Stalagmite evidence for the onset of β- counting of the gaseous phase, with a “Beta of the Last Interglacial in southern Europe at 129 ± Logic” proportional counter, using ethane obtained by 1 ka. 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International Journal of Speleology, 37(3), 153-172. Bologna (Italy). October 2008